I have researched this as I’ve just booked NRT-SYD at the beginning of November. Here are the key points:
JAL release availability for all flights including redemptions 330 days out.
They are released at 10am Japan time which is 1am GMT
2 J and 4 W are released for each flight.
Apparently 2 F are also released but my route didn’t have this so I can’t confirm.
ba.com is the best place to snaffle the awards as it updates in real time.
Ironically, the seats are available on ba.com before they are available to Mileage Bank members.
More seats are made available closer to departure.

Hope this helps!